The present disclosure relates to a method and apparatus to permit changing a filter on the input line to a vacuum deposition chamber without breaking or reducing the vacuum for the deposition chamber or for the rest of the deposition system.
In thin film deposition for semiconductor applications, it is often necessary to vaporize a precursor chemical in liquid or solid form to generate a vapor. Film deposition can then take place by a vapor phase process such as chemical vapor deposition (CVD), atomic layer deposition (ALD), and other known processes. A carrier gas is often introduced into the vaporization apparatus to form a gas/vapor mixture to meet specific processing requirements.
Vaporization of a liquid or solid precursor to form vapor is often accompanied by the formation of particles. These particles may range in size from a few nanometers (nm) in diameter to hundreds or thousands of nanometers. Particles carried by the gas/vapor mixture into the deposition chamber can deposit on the wafer surface causing harmful effects, including the loss of product yield. Product yield loss due to particulate contamination is a major cause of decreased product output in a semiconductor device fab. Left uncontrolled, particulate contamination can severely impact the productivity and profitability of the device fab.
One known method of reducing particulate contamination of wafers is to place a filter in the incoming process gas stream to remove particles and prevent them from being carried by the stream into the deposition chamber. Precursor vaporization systems such as those described in U.S. Pat. No. 6,409,839 includes a filter for particle removal, thus insuring that the output gas/vapor mixture will be substantially free of particulate contamination. Since hot vapor can condense in a cold filter, the filter must be heated. The vaporization apparatus described in U.S. Pat. No. 6,409,839 has a built-in filter that is heated to substantially the same temperature as the remaining parts of the system, thus minimizing potential vapor condensation on an unheated or insufficiently heated filter.
One consequence of using a filter in a film deposition apparatus, also referred to as a tool, is that the filter can get clogged during use due to particle accumulation in the filter. A clogged filter will cause an increase in filter pressure drop. A clogged filter can also cause particle shedding, resulting in particles collected on the filter being re-entrained by the gas/vapor flow, and resuspended in the mixture stream. These re-entrained and resuspended particles reappear as gas-borne particulate contaminant downstream of the filter and thus are carried by the mixture flow into the deposition chamber to contaminate the wafer placed therein. When this happens, the filter must be removed and replaced.
Replacing a filter in the vaporization apparatus or tool will require removing a clogged filter and replace it by a new one. In the case of the vaporization apparatus including a filter described in U.S. Pat. No. 6,409,839, the entire vaporizer or vaporization apparatus must be removed from the system. Removing a filter or a vaporizer from a film deposition tool, will require shutting down the tool resulting in the loss of productive use of the tool time for film deposition and device fabrication purposes. U.S. Pat. No. 6,409,839 does show vaporizer apparatus or mechanisms, and is incorporated by reference.
Shutting down a film deposition tool operating under vacuum generally requires breaking the system vacuum and returning the tool to atmospheric pressure in order for the filter to be removed and replaced. When a filter or a vaporizer is removed from a tool, normal ambient air in the cleanroom will enter into the deposition chamber causing various system components in fluid communication with the chamber to be exposed to contaminant gases brought in by ambient cleanroom air. Gaseous contaminants such as oxygen, water vapor, CO2, SO2, etc. that are present in small or trace amounts will thus enter the vacuum system causing the interior surfaces of the system to be coated with the molecules of the contaminant gas. Many of these contaminant gases are harmful to the semiconductor integrated circuit devices being fabricated and must be removed thoroughly before film deposition and device fabrication can resume. Contaminant molecules adhering to the interior surfaces of the vacuum system by physical adsorption or chemical absorption are difficult to remove. Their removal requires pumping down the system to a high vacuum for an extended period of time to permit the adsorbed contaminant gases to be desorbed or out gassed from the surfaces. The desorbing or out gassing process can take many hours to several days to complete. During this time, the deposition tool would sit idle and not used for production. The resulting loss of the productive use of the tool may be quite severe when many tools in a semiconductor device fab need to be shut-down for filter removal or maintenance.